
'''
海伦公式求三角形面积
p = (a+b+c)/2
S = sqrt(p * (a-p) *(b-p) * (c-b))

内切圆的半径：r=2S/L = 2S/(a+b+c)

'''


import math

a = int(input('请输入边长a：'))
b = int(input('请输入边长b：'))
c = int(input('请输入边长c：'))

if a>0 and b>0 and c>0 and (a+b)>c and (a+c)>b and (b+c)>a:

    p = (a+b+c)/2
    s = math.sqrt(p * (a-p) *(b-p) * (c-b))
    r = 2*s/(2*p)
    sc = math.pi * r**2
    print(sc)


else:
    print("请正确输入三角形三边")